216P - Spatial transcriptomics reveals tumor-microenvironment heterogeneity of breast cancer

Background

A previous pan-cancer single-cell study on the tumor microenvironment (TME), particularly tumor-infiltrating lymphocytes (TILs), highlighted both the heterogeneity and dynamics of various T cell subtypes. However, the spatial heterogeneity of TILs in breast cancer has not been extensively studied. We aimed to investigate the spatial heterogeneity of the TME using spatial transcriptomics.

Methods

We retrospectively collected FFPE samples from five breast cancer cases (2 triple-negative breast cancer [TNBC] with high TILs, 2 TNBC with low TILs, 1 hormone receptor-positive[HR+] breast cancer with TIL high TILs) and performed the Visium Spatial Gene Expression method (10x Genomics). Subsequently, using public TILs single-cell data from a pan-cancer study, we predicted and annotated cell types in each Visium spot (single cell deconvolution). We studied the distribution of T cell subtypes across three layers at 3mm intervals from the most peripheral to the central direction of the tumor.

Results

The distribution of 24 CD4+ subtypes and 17 CD8+ subtypes was examined. In all five cases, the CD8.c.12.Tex.CXCL13 subtype showed a statistically significant increase in cell numbers at the tumor center compared to the periphery. The CD4.c20.Treg.TNFRSF9 subtype displayed a similar trend, with higher cell counts in the tumor center and lower counts in the periphery. Conversely, the CD8.c10.Trm.ZNF683 subtype, a key subtype in the previous pan-cancer study, exhibited varying distribution patterns between cases.

Conclusions

TILs in breast cancer consist of diverse subtypes. Numerical heterogeneity was observed among T cell subtypes, along with spatial heterogeneity between the tumor’s central and peripheral regions. Furthermore, heterogeneity was evident between individual tumors. However, some consistent distribution patterns, such as the CD8.c.12.Tex.CXCL13 population, were also observed across cases. Further studies are needed to determine the clinical significance of this spatial heterogeneity.

Legal entity responsible for the study

The authors.

Funding

Has not received any funding.

Disclosure

All authors have declared no conflicts of interest.